But he scored a big laugh from the backbenchers when he told Sir Menzies he "door is always open", less than a fortnight after he tried to coax senior Lib Dems into government.

Mr Brown said his government would seek to make housing affordable and said this would need more houses to be built.

He said this would require local authorities to release land for building and called on Tory-controlled local authorities to lift their resistance to new building projects.

Mr Brown has spoken of the need to improve the quality of childhood. He praised organisations working to stamp out bullying and said he was very fortunate to have attended the launch of anti-bullying week.

The prime minister revealed the children secretary Ed Balls will announce £30 million of funding for Childline over the next two years.

He also confirmed the health secretary Alan Johnson would unveil plans for further NHS reform, after he pledged to make the health service "a priority" in government.

Although the new prime minister has promised to lead a change in government, he committed himself to some of his predecessor's key policies.

He refused to commit to a date removing UK troops from Iraq, saying it would be wrong to set a timetable at this stage.

Mr Brown said the UK had already cut troop levels to 5,500 in Iraq, with plans for further withdrawals when feasible, and had moved from combat to over-watch duties in three provinces.

He also affirmed the government's commitment to nuclear power and plans for a new generation of nuclear power stations.

Mr Brown said it should have been made clear over the past few years that the UK cannot rely on an energy policy that leaves it dependent on one or two regions.

The prime minister ducked Sir Menzies call to reopen the Serious Fraud Office investigation into the BAE-Saudi arms case, insisting the decision to prosecute was not for the government.

He also rejected Lib Dem calls to reform council tax, interpreting their poor electoral result as proof of the public's lack of enthusiasm for a local income tax.